Homocysteine modifies development of neurulation and dorsal root ganglia in chick embryos

Background: The formation of the neural tube (neurulation) involves two mechanisms: primary and secondary neurulation. In chicks, there is also an overlap zone, where both mechanisms work together. Homocysteine (Hcy) may have an important teratogenic role in neural tube defects (NTD) when folic acid levels are considered normal. Recently, Hcy capability to generate NTD and modify neural crest cell migration has been demonstrated in chick embryos. This study was aimed to evaluate the effects of Hcy on neurulation and the development of the dorsal root ganglia (DRG). Methods: Chick embryos were treated with L-Hcy thiolactone 20 mumol to produce the highest rate of survival with embryos carrying neural tube defect (NTD) in the spine. Embryos at stages (st) 3-10 were treated and harvested at st 18-23. Only externally normal embryos or those carrying spinal NTD embryos were considered. Results: Histological sections of Hcy-treated embryos showed: open spina bifida (39% of embryos), more than one tube forming the spinal cord (26%), disorganized spinal cord (26%), always affecting lumbosacral regions, probably in the overlap zone. Additionally, 32% of embryos had small and continuous DRG, associated with a slimmed roof plate. Three-dimensional reconstruction showed unsegmented DRG until the C8 ganglion level. There was a 75% reduction of C3 DRG cells in treated embryos in comparison to untreated ganglia. Conclusion: Hcy teratogenicity in avian embryos affected the neural tube in the overlap zone, secondary neurulation and the cervical DRG. (C) 2002 Wiley-Liss, Inc.